This invention relates to concrete screed rails, which are increasingly being accepted by the construction industry in place of traditional shuttering or formwork to assist in the placing of in situ concrete slabs and screeds.
Wooden formwork suffers from the disadvantages that it has to be sawn to size and assembled by carpenters on site, and then struck (i.e. stripped out) after a concrete pour has partly cured. It is therefore time consuming to use, and hence expensive. Furthermore, it can normally be used only once, and then becomes scrap.
The main advantage of concrete screed rails is that they are formed of the same material as t he finished slab, and can therefore be left in position to form part of the slab. They also ensure that top quality concrete is provided at a slab edge, and when left in situ, they ensure a good bond with the adjacent concrete pour. Furthermore, they are easy to use, especially with reinforcement rods, and save up to 50% in time compared with timber formwork.
Concrete screed rails are already known, but these are heavy to handle and transport and are costly to transport. One known type of rail has preformed apertures in the web between the top and bottom flanges for the passage of reinforcement bars, dowels, pipework and other conduit (see EP-A-0168205 and WO/81/02600), but in practice the apertures are of the wrong size or in the wrong location. This problem is normally overcome by knocking out, with a hammer, part of the web, which will result in poured concrete leaking through the rail, and perhaps significantly weakening the rail. One version of this type of rail is known as the PERMABAN leave-in-place screed rail.
Another known concrete screed rail, the subject of EP-B-0124532, has preformed apertures in its web, and areas of reduced thickness concrete called knock-outs, which can be removed by knocking away the concrete with a hammer; again, too much concrete is usually removed, which causes leakage of poured concrete.
It has also been proposed in GB-A-480259 to produce a concrete screed rail with preformed, spaced apertures for the passage of reinforcement rods, and recesses formed in each face of the web of the rail so that it will form a key with the concrete poured on either side of the rail.
We have now developed a concrete screed rail which has all the advantages of known concrete screed rails, but does not suffer from the major disadvantages associated with such known screed rails.